1. Field of the Invention
The invention generally relates to handling connection release procedures, and more particularly, to apparatuses and methods for handling a network initiated connection release procedure for users receiving multimedia broadcast and multicast services (MBMS) services.
2. Description of the Related Art
In a typical mobile communication environment, a user equipment (UE) may communicate voice and/or data signals with one or more service networks via cellular stations of the service networks. The wireless communications between the HE and the service networks may be in compliance with various wireless technologies, such as the Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, Code Division Multiple Access 2000 (CDMA 2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, and others. The Radio Resource Control (RRC) state of the User Equipment (UE) can be either an idle mode (RRC_IDLE) or a connected mode (RRC_CONNECTED). When an RRC connection is established, the UE leaves the idle mode and enters the connected mode, and when a RRC connection is released the UE leaves the connected mode and enters the idle mode. In other words, a UE is in a connected mode when an RRC connection has been established and the UE is in an idle mode if no RRC connection is established.
A UE in the idle mode may further perform cell selection and reselection to decide which cell to camp on. The cell (re)selection process takes into account the priority of each applicable frequency of each applicable Radio Access Technology (RAT), the radio link quality and the cell status (i.e. whether a cell is barred or reserved). A UE in the idle mode may further monitor a paging channel to detect incoming calls, and also acquires system information. The system information mainly consists of parameters by which the network can control the cell (re)selection process.
Take the LTE technology for example. After a UE is powered on, it will need to perform a connection establishment procedure to connect to the LTE network so that it can obtain packet data services from the LTE network. The purpose of the connection establishment procedure is to establish a (RRC) connection. As shown in FIG. 1, the connection establishment procedure starts by the UE transmitting a CONNECTION REQUEST message to the LTE network to request the establishment of an RRC connection (step S110). When receiving the CONNECTION REQUEST message, the LTE network checks if the establishment cause and loading of the network, e.g. the load of eNB, matched. If none of the checks fail, the LTE network accepts the connection request by transmitting a CONNECTION SETUP message to the UE (step S130). In response to the CONNECTION SETUP message, the UE establishes the logical links and bearers according to the configuration information (step S140), and transmits a CONNECTION SETUP COMPLETE message to the LTE network (step S150), to acknowledge that it has received the CONNECTION SETUP message and confirm the successful completion of the RRC connection establishment. If the CONNECTION SETUP COMPLETE message is received successfully, the connection establishment procedure ends. Later, a connection release procedure may be initiated to release the established connection from the LTE network.
No matter the UE is in connected mode or idle mode, a UE that interests in MBMS service will base on MBSENAreaConfiguration message to configure MBMS radio resources. Specially, the UE may first receive system information to get the MCCH configuration, obtain the MBSFNAreaConfiguration message on MCCH, and then obtain MBMS radio resources configurations, i.e. MTCH information from this message.
FIG. 2 is a message sequence chart illustrating a connection release procedure initiated by a LTE network. The connection release procedure may be initiated by a LTE network for various reasons, such as due to a completion of transaction between the user equipment and the core network, an unspecified failure, user inactivity, loss of radio connection with UE and the like. To begin, the LTE network first transmits a CONNECTION RELEASE message to the UE to request the UE to release the RRC connection from the LTE network (step S210). When receiving the CONNECTION RELEASE message, the UE releases the established logical links and bearers for the packet data services (step S220).
The connection release procedure is used to release an established connection, which includes the release of established radio bearers as well as all radio resources. In other words, the UE will release all the radio resources when leaving the connected mode.